The present invention relates to a joint for interconnecting two electrical cables, each cable comprising a central conductor, an insulation layer, a semi-conductive coating layer, a metallic cable screen and an outer cable jacket, all bared over predetermined lengths, the joint being adapted to ensure the interconnection of the conductors and including mechanically shrink-fittable materials adapted to ensure, when shrunken, a dielectric continuation of the insulation layer, a continuation of the cable screen by means of a metallic joint screen, and an outer protection.
Such a cable joint is generally known in the art, and the present invention will particularly concentrate on the screen continuation of the cables.
The screen continuity should go from the end of a cable over the joint to the end of the other cable. In the joint, a part of the metallic grounding screen of the cable is cut away over a length of more than 30 cm to 60 cm. This part has to be reconstructed. The joint itself is therefore equipped by a screen of wires with a sufficient section, with more than the original section of the cable screen. The goal is to obtain a good connection of the cable screen with the joint screen. A cold shrinkable joint, also called "mechanically shrink-fittable" joint, is pre-assembled in the factory and, for easy and quick installation, the outer protection thereof should cover the complete cable connection, i.e. should also include the screen connection. So, during--and after--installation of the joint, the access to the screen connection is difficult because it will be covered by the outer protection of this joint.
The technical problem is to find a quick installable and adequate screen connection developed according to existing standards. This requires a screen connection with sufficient contact pressure and contact surface between the cable screen and the joint screen to guarantee a resistance of the whole screen connection that is as low as possible. The reason therefore, is to avoid heat build-up and damage on the outer cable jacket and/or on the semi-conductive coating layer. Furthermore, the screen connection should be as cheap as possible.
Such a screen connection is generally realized by using a so-called "roll-spring", e.g. the "Rollfedern Typ RF" of the German company CELLPACK GmbH--Electrical Products, located at D-79761 Waldshol-Tiengen. A roll-spring is a spiral-winded ribbon of steel that is placed around the bared metallic screen of the cable before the installation of the joint.
The roll-spring is used to increase the contact surface between the cable screen and the joint screen, especially when these screens are made of wires, as is generally the case. However, since the roll-spring is made of steel, it has a relatively high electrical resistance. The steel ribbon also has a limited width whereby the whole length of the bared cable screen is not covered. Due to the differences of thickness of the parts of the cable screen covered and not covered by the roll-spring, it is difficult to ensure a good electrical contact with the joint screen. As a result, the cable may be damaged because of poor electrical contacts that can cause a bad screen connection and/or an electrical failure of the joint. Also the installation of the spring is not easy because the spiral has to be opened in order to be wound around the cable. Moreover, in order to improve the electrical contact between the cable screen and the joint screen, these screens are placed between different layers of the steel spiral. However, the joint screen can only be inserted into the spiral when the joint has been shrunken over the cables. The outer protection of the joint has then to be removed, at least partially. This operation may reduce the sealing effect of the outer protection of the joint and is time consuming. The roll-spring further has very cutting edges which can damage parts of the joint during installation. It can cut the outer protection of the joint, during and after installation. During installation, it can for instance also cut the sliding film of the supporting tube of the joint.